Many factories use compressed air as a major source of power for operating their production machinery. The air is typically supplied from on-site or nearby compressors and piped to a downstream use or demand area through a distribution system, with pressure-stabilizing storage means being provided upstream, in the form of tanks or receivers. Typical equipment includes pneumatically powered machine tools, drills, wrenches, presses and lathes, as well as mills and buffers, and low demand spray booths and instrumentation. Such equipment is commonly referred to in the art as the "article", a generic term connoting anything connected to the air system to make use of the supply.
End users want the air system to maintain adequate pressure to run their air-powered equipment and few consider the energy costs of the air.
Major changes in downstream demand create varying loads on the compressors. Air compressors are typically controlled according to system supply pressure, coming on-line as system pressure at the compressor, or nearby, drops below a threshold pressure and going off-line at a higher cutout pressure. This is necessarily a rather crude control system, especially as air compressors are slow to respond to changes. As factory production drops off, for example at the end of a shift, air demand declines, and this decline can be quite sudden.
System pressure rises substantially to unload compressor horsepower until compressor output can be adjusted and this overpressure can increase the air consumption rate as still-operating machinery uses more air and also increases leakage. These overpressure losses constitute an artificial demand resulting in wasted energy. Being designed to maintain a threshold working pressure under conditions of heavy demand, most air systems use an excess of compressor capacity over the theoretical capacity needed to give satisfactory operational results, with consequent unnecessary capital expenditure and running costs.
Prior art pneumatic control systems generally depend upon the above-described crude compressor switching together with pressure regulators operating at the article to protect individual pieces of equipment from pressure surges. Such regulators can be controlled from downstream pressure detectors with a feedback loop and typically discharge overpressures to atmosphere.
In general, the prior art uses local control with little if any thought given to overall system control. In general, the prior art has paid little, if any attention to overall system efficiency. Indeed, it has been a surprising observation relating to the genesis of the present invention that most operators set their regulator valves to maximum, probably in the belief that they will get more performance out of their equipment. Such operators display little regard for system efficiency and equipment durability.
These rather simple control devices merely provide a preliminary level of control and do little if anything to improve the overall system efficiency. Other substantial drawbacks associated with the use of such downstream flow controllers are that mechanical and pneumatic inertia, or hysteresis, slow the responsiveness of the system allowing, substantial abnormalities and consequent air, or energy, losses to develop.